[求助]GWD-13-11, gwd-13-15

11.   One of four babies are now born to mothers aged thirty years or more, compared with just one of six born in 1975.

(A) of four babies are now born to mothers aged thirty years or more, compared with just one of six born

(B) of four babies is now born to a mother whose age is thirty or older, compared to just one of six babies who were born

(C) baby in four are now born to mothers aged thirty or older, compared to just one in six

(D) baby in four is now born to a mother aged thirty or older, compared with just one in six（D）

(E) baby in four is now born to mothers aged thirty years or more, compared to just one in six

I would like to ask what is wrong in B? And I would also like to now which one is correct? is or are after one of four babies?

(A) tell individual genes both when to become active and when to remain

(B) tell individual genes both at which time they should become active or should remain

(C) tells individual genes both when to become active or remain

(D) tells individual genes both when to become active or when to remain（A）

(E) will tell an individual gene both about when it should become active and remain

Why in this question 'one of sth' use tell but not tells?

Thanks a lot.

D

'One in four' is more appropriate to indicate a ratio than 'one of four'. 

because the thing believed is not the only substance that could tell.

btw, the other choices could all be easily eliminated.

understood, thanks a lot.